The present invention relates generally to SS7 signalling and more particularly to a method and apparatus for distributing the Message Transfer Part (MTP) Level 2 functionality between a Signalling Gateway and a Media Gateway.
The following acronyms will be used throughout this document:
A Public Switched Telephone Network (PSTN) is, conventionally, comprised of two networksxe2x80x94a voice/data network and a signalling network. The signalling network carries information for call set-up and tear down. The Common Channel Signalling System #7 (CC-SS7) protocol is used for call set-up and tear down.
As is known in the art, the PSTN provides users with a dedicated, end-to-end circuit connection for the duration of each call. The circuits are reserved between the originating call, tandem switches (if any), and the terminating switch based on the called party number. In a typical Intelligent Network (IN), such as the North American SS7 network, to set-up a basic call circuit between a calling party at a first Service Switching Point (SSP), and a called party, having an out-of-switch number (i.e., the called party is at a second SSP), SS7 messages are exchanged between the two SSPs using the SS7 network.
Recent developments, notably the popularity of the Internet, have increased the use of Voice over IP (VoIP) communication. Voice over IP switches need to interface to the existing PSTN networks (voice and signalling) to allow PSTN phones to use the VoIP network. A VoIP switch would interface to the PSTN Voice network using a Media Gateway. The Media Gateway provides the translation between Time Division Multiplexed (TDM) data and IP packet data. This VoIP switch would interface to the PSTN Signalling network using a Signalling Gateway. The Signalling Gateway provides the translation between SS7 and IP.
In a quasi-associated SS7 signalling network, the Signalling Gateway would connect to the local STP mated pair using A-links. In a fully associated SS7 Signalling network, the signalling gateway would connect directly with the SSPs using F-links. In the fully associated network signalling case, the SS7 signalling link is usually carried over the same facilities as the voice trunks. Since these voice trunks terminate on the media gateway, external circuitry (e.g. channel banks) are required to extract the signalling channel and route it to the signalling gateway. Moreover, since the media and signalling gateways are typically geographically quite dispersed, the equipment associated with transmitted the extracted signalling channel to the signalling gateway is expensive.
Accordingly, it is desired to provide a system which addresses some of these shortcomings.
This invention distributes the MTP Level 2 functionality between the Signaling Gateway and the Media Gateway. It allows F-links in a fully associated SS7 signaling network to be terminated on the Media Gateway and the SS7 messages to be passed between the Media Gateway and the Signaling Gateway over IP.
According to one aspect of the invention, there is provided a method providing distributed Message Transfer Part (MTP) functionality over an Internet Protocol (IP) network, said method comprising: at a first media gateway: receiving conventional MTP signalling units from a first network element; removing repeated MTP signalling units from said MTP signalling units received; either before or after said removing, encapsulating received MTP signalling units into data packets to form a reduced signalling unit packet stream; transmitting said reduced signalling unit packet stream to a signalling gateway; receiving at said signalling gateway said reduced packet stream at said signalling gateway; transmitting packets encapsulating MTP signalling units to one of said first media gateway and a second media gateway, said transmitted packets being responsive to said received reduced signalling unit packet stream; receiving at said one of said first media gateway and said second media gateway said packets transmitted by said signalling gateway; and at said one of said first media gateway and said second media gateway, re-creating conventional MTP signalling units based on said routed packets and transmitting said re-created conventional MTP signalling units to one of said first network element and a second network element.
According to a further aspect of the invention there is provided a Voice over Internet Protocol (VoIP) switch providing a distributed Message Transfer Part Level 2 (MTPL2) protocol, said VoIP switch comprising: a plurality of media gateways, each of said media gateways in communication with a conventional SS7 physical link, said conventional SS7 physical link in communication with a network element; a signalling gateway; an IP network providing IP communication between said plurality of media gateways and said signalling gateway.
According to a still further aspect of the invention there is provided a media gateway comprising: a receiver for receiving a contiguous stream of signalling units from a network element; a filter for discarding repeated signalling units in said received stream; an encapsulated data transmitter adapted to transmit data encapsulating said signalling units over a packet switched network; an encapsulated data receiver adapted to receive encapsulated data encapsulating signalling units from a packet switched network; a processor adapted to: encapsulate signalling units forming said stream of signalling units either before or after said discarding by said filter; and de-encapsulate signalling units received by said encapsulated data receiver and generate signalling units to re-create a contiguous stream of signalling units; and a signalling unit transmitter transmitting a re-created contiguous stream of signalling units to a network element.
According to a still further aspect of the invention there is provided a signalling gateway comprising: an encapsulated data receiver for receiving encapsulated signalling units from a packet switched network; an encapsulated data transmitter adapted to transmit data encapsulating signalling units over a packet switched network; a processor adapted to: de-encapsulate said received encapsulated signalling units and generate signalling units compliant with the Message Transfer Part Level 2 protocol; transmit said generated signalling units to a Message Transfer Part Level 3 processor; receive conventional signalling units from said Message Transfer Part Level 3 processor; and encapsulate said received conventional signalling units for transmission by said encapsulated data transmitter.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.